//给定一个 n 叉树的根节点 root ，返回 其节点值的 前序遍历 。 
//
// n 叉树 在输入中按层序遍历进行序列化表示，每组子节点由空值 null 分隔（请参见示例）。 
//
// 
//示例 1： 
//
// 
//
// 
//输入：root = [1,null,3,2,4,null,5,6]
//输出：[1,3,5,6,2,4]
// 
//
// 示例 2： 
//
// 
//
// 
//输入：root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,
//null,13,null,null,14]
//输出：[1,2,3,6,7,11,14,4,8,12,5,9,13,10]
// 
//
// 
//
// 提示： 
//
// 
// 节点总数在范围 [0, 10⁴]内 
// 0 <= Node.val <= 10⁴ 
// n 叉树的高度小于或等于 1000 
// 
//
// 
//
// 进阶：递归法很简单，你可以使用迭代法完成此题吗? 
// Related Topics 栈 树 深度优先搜索 👍 252 👎 0

package leetcode.editor.cn;

import java.util.*;

public class _589_NAryTreePreorderTraversal {
    public static void main(String[] args) {
        Solution solution = new _589_NAryTreePreorderTraversal().new Solution();
        Node root = new Node(1);
        List<Node> tmp = new ArrayList<>();
        tmp.add(null);
        tmp.add(new Node(5));
        tmp.add(new Node(6));
        root.children = new ArrayList<>();
        root.children.add(null);
        root.children.add(new Node(3, tmp));
        root.children.add(new Node(2));
        root.children.add(new Node(4));

        List<Integer> res = solution.preorder(root);
        System.out.print("result:");
        for (int num : res) {
            System.out.print(num + " ");
        }
        System.out.println();
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    // Definition for a Node.
    private static class Node {
        public int val;
        public List<Node> children;

        public Node() {
        }

        public Node(int _val) {
            val = _val;
        }

        public Node(int _val, List<Node> _children) {
            val = _val;
            children = _children;
        }
    }


    class Solution {
        public List<Integer> preorder(Node root) {
            List<Integer> res = new ArrayList<>();
            if (root == null) {
                return res;
            }

            Deque<Node> st = new ArrayDeque<>();
            st.push(root);
            while (!st.isEmpty()) {
                Node node = st.pop();
                res.add(node.val);
                if(node.children != null) {
                    for (int i = node.children.size() - 1; i >= 0; i--) {
                        if (node.children.get(i) != null) st.push(node.children.get(i));
                    }
                }
            }
            return res;
        }
    }


    class Solution2 {
        public List<Integer> preorder(Node root) {
            List<Integer> res = new ArrayList<>();
            if (res == null) return res;

            Node node = root;
            Deque<Node> st = new ArrayDeque<>();
            HashMap<Node, Integer> map = new HashMap<>();
            while (!st.isEmpty() || node != null) {
                while(node != null) {
                    res.add(node.val);
                    st.push(node);
                    List<Node> children = node.children;
                    if (children != null && children.size() > 0) {
                        map.put(node, 0);
                        node = children.get(0);
                    } else {
                        node = null;
                    }
                }
                node = st.peek();
                int index = map.getOrDefault(node, -1) + 1;
                List<Node> children = node.children;
                if (children != null && children.size() > index) {
                    map.put(node,index);
                    node = children.get(index);
                } else {
                    st.poll();
                    map.remove(node);
                    node = null;
                }
            }
            return res;
        }
    }

    // 通过了，这是递归调用
    class Solution1 {
        private List<Integer> res = new ArrayList<>();

        public List<Integer> preorder(Node root) {
            if (root != null) {

                res.add(root.val);
                List<Node> children = root.children;
                if (children != null) {
                    for (Node node : children) {
                        preorder(node);
                    }
                }
            }
            return res;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}